Nematodes are non-segmented, bilaterally symmetric, worm-like invertebrates that possess a body cavity and complete digestive system but lack respiratory and circulatory systems. Their body wall contains a multilayer cuticle, a hypodermis with four longitudinal cords, and internal musculature (Chitwood, D. J. (2003). Nematicides. Encyclopedia of Agrochemicals, vol 3. J. R. Plimmer. New York, John Wiley & Sons. 3: 1104-1115). Their body contents are mostly occupied by digestive and reproductive systems. Nematodes may be classified as either parasitic or free living. Parasitic nematodes may be classified by their hosts (e.g., plant parasites). Free living nematodes may be classified according to their feeding habits and include the following groups: (1) omnivores; (2) bacterial feeders; (3) fungal feeders and (4) predators.
Plant parasitic nematodes generally feed on underground parts of plants, such as roots, bulbs, and tubers as well as above ground parts of the plants, such as leaves and stems. Annual crop losses caused by plant-parasitic nematodes have been estimated to exceed US $100 billion (Koenning, S. R., Overstreet, C. et al. (1999). Journal of Nematology 31: 587-618). Examples of plant parasitic nematodes include but are not limited to nematodes belonging to Meloidogyne spp. (e.g., root-knot nematodes); Pratylenchus spp. (e.g., lesion nematodes); Heterodera spp. (e.g., cyst nematodes); Globodera spp. (cyst nematodes); Ditylenchus spp. (e.g., stem and bulb nematodes); Tylenchulus spp. (e.g., citrus nematodes), Xiphinema spp. (e.g., dagger nematodes); Radopholus spp. (burrowing nematodes); Rotylenchulus spp. (e.g. reniform nematodes); Helicotylenchus spp. and Scutellonema spp. (e.g. spiral nematodes); Belonolaimus spp. (e.g., sting nematodes); Bursaphelenchus spp. (e.g. pine wilt nematodes); Hoplolaimus spp. (lance nematodes); Longidorus spp. (needle nematodes); Nacobbus spp. (false root-knot nematodes); and Aphelenchoides spp. (foliar nematodes). The most efficient means for controlling nematodes is via nematicides that inhibit egg hatching, juvenile motility and/or plant infectivity. The development of chemical control for plant-parasitic nematodes is challenging because of both environmental and physiological reasons: (1) most phytoparasitic nematodes live in a confined area in soil near the roots and hence, delivery of a chemical nematicide is difficult and (2) the outer surface of nematodes is a poor biochemical target, and is impermeable to many organic molecules (Chitwood, D. J. (2003). Nematicides. Encyclopedia of Agrochemicals, vol 3. J. R. Plimmer. New York, John Wiley & Sons. 3: 1104-1115). Moreover, delivery of toxic compounds by an oral route is nearly impossible because most plant parasitic nematode species ingest material only after they have penetrated and infected plant roots. Therefore, nematicides have tended to be broad-spectrum toxins with high volatility or with other chemical and physical properties promoting their motility in soil.
According to Sasser and Freckman (In J. A. Veech and D. W. Dickson (Eds.), Vistas on Nematology, 1987, (pp. 7-14). Society of Nematologists, Hyattesville), crop losses by nematodes range from 8 to 20% on major crops around the world. Plant parasitic nematodes can cause considerable crop damage with annual losses estimated at $87 billion worldwide (Dong, L. Q. and Zhang, K. Q. (2006) Plant Soil 288:31-45). Fumigants such as methyl bromide are very effective in controlling both soil-borne plant diseases and nematodes but due to the high mammalian toxicity, ozone depleting effects and other residual effects, the use of methyl bromide has already been banned in various countries and its complete withdrawal from the market is planned by international agreement (Oka, Y., Nacar, S. et al. (2000). Phytopathology 90:710-715). Chemical alternatives such as methyl iodide, 1,3-Dichloropropene, and chloropicrin also have issues with mammalian and environmental safety. Chemical non-fumigant nematicides are being phased out and banned. Most recently, the US-EPA announced that aldicarb will be phased out.
Accordingly, there is currently a need for additional nematicides; in particular, those with maximal nematode-specific toxicity. In addition, in light of the ever-increasing resistance of plant pathogens to synthetic pesticides, and the environmental concerns associated with chemical pesticide use, there is a need for new, naturally-occurring pesticides (e.g., biopesticides) to which plant pathogens have not developed resistance, and which have minimal environmental effects.